1. Field of the Invention
This invention relates to a method of detecting a test body with a sensor utilizing a localized plasmon resonance phenomenon.
2. Description of the Related Art
As sensors utilized for detection or identification of substances or for examination concerning molecular structures, sensors utilizing a localized plasmon resonance phenomenon have heretofore been known. The sensors utilizing the localized plasmon resonance phenomenon utilize a device having a structure, in which fine metal particles are secured in a layer-shaped form to a surface of a dielectric material, as a sensor chip. Also, the sensors are constituted of means for irradiating light to the layer of the fine metal particles of the sensor chip, and means for spectrophotometrically detecting the light, which has been reflected from the layer of the fine metal particles, and measuring the intensity of each of light components having different wavelengths.
In cases where light is irradiated to fine metal particles smaller than the wavelengths of the light, free electrons within the fine metal particles resonate with an electric field of a light component having a specific wavelength and begin to vibrate. The phenomenon described above is referred to as the localized plasmon resonance phenomenon. In cases where the electrons within the fine metal particles begin to vibrate, and the localized plasmon resonance is induced, strong electric fields occur around the fine metal particles, and the scattering and the absorption of the light component having the specific wavelength (hereinbelow referred to as the resonance wavelength) are caused to increase markedly.
In such cases, the resonance wavelength depends upon the refractive index of a substance, which is present around the fine metal particles. Specifically, in cases where the refractive index of the substance, which is present around the fine metal particles, is large, a resonance wavelength shifts to the long wavelength side, and the scattering and the absorption of the reflected light increase. Therefore, in cases where the irradiation of the light and the measurement of the intensity of the reflected light are performed in a state, in which a substance acting as a test body is capable of being adsorbed to the layer of the fine metal particles or accumulating on the layer of the fine metal particles, the test body is capable of being detected in accordance with a marked alteration in intensity of the reflected light. Also, the kind of the test body is capable of being specified in accordance with the wavelength, which is associated with the occurrence of the marked alteration in intensity of the reflected light. As the sensor chip for use in the sensors described above, for example, a sensor chip comprising a base body and a colloidal metal single-layer film, which is formed at a surface area of the base body, has heretofore been known. The sensor chip comprising the base body and the colloidal metal single-layer film, which is formed at the surface area of the base body, is described in, for example, Japanese Unexamined Patent Publication No. 2000-356587.
Also, as a technique for detecting a test body, which has been dispersed in a liquid, by use of a sensor chip of the type described above, there has been proposed a technique wherein, besides the fine metal particles having been fixed to the sensor chip, fine metal particles are bound to the side of the test body. (The proposed technique for detecting a test body is described in, for example, “Metal Nanoparticles, Synthesis, Characterization, and Applications,” Daniel L. Feldheim, Colby A. Foss, Jr., MARCEL DEKKER Inc., pp. 183-205.) With the proposed technique for detecting a test body, at the time at which the test body has been adsorbed to the surface of the sensor chip, a fine metal particle on the side of the sensor chip and a fine metal particle on the side of the test body are located close to each other. The resonance wavelength of the localized plasmon resonance varies in accordance with the state, in which the fine metal particles are located close to each other. Therefore, in cases where the fine metal particles are bound to the side of the test body, the variation in resonance wavelength is capable of being found easily.
With the sensor chip disclosed in Japanese Unexamined Patent Publication No. 2000-356587, the problems are encountered in that the colloidal particles are apt to agglomerate, and therefore the sensor chip is difficult to produce, and in that the sizes of the fine metal particles are not uniform. As a technique for solving the problems described above, there has been proposed a technique, wherein regularly arrayed fine holes are formed previously on a base plate, fine metal particles are filled respectively in the fine holes, and a sensor chip of the type described above is thereby produced. (The technique for producing a sensor chip is described in, for example, Japanese Unexamined Patent Publication No. 2003-268592.)
The fine structure body disclosed in Japanese Unexamined Patent Publication No. 2003-268592 has the advantages over the sensor chip disclosed in Japanese Unexamined Patent Publication No. 2000-356587 in that the fine metal particles having uniform size are arrayed regularly, and in that reliable measurement results are capable of being obtained. However, with the fine structure body disclosed in Japanese Unexamined Patent Publication No. 2003-268592, wherein each of the fine metal particles is located in the interior of one of the fine holes, in cases where the technique for detecting a test body described in the aforesaid literature entitled “Metal Nanoparticles, Synthesis, Characterization, and Applications” is to be utilized, the problems are encountered in that it is difficult for a fine metal particle on the side of the sensor chip and a fine metal particle on the side of the test body to be located close to each other. Specifically, for certain types of sensing techniques, it often occurs that the fine structure body disclosed in Japanese Unexamined Patent Publication No. 2000-356587 is more appropriate than the fine structure body disclosed in Japanese Unexamined Patent Publication No. 2003-268592.